A216529 Numbers n such that (10^n-1)/9 is prime and can be written in the form a^2 + 3*b^2.

19, 49081, 109297, 270343

Offset

1,1

Comments

The exponent is congruent to 1 mod 3.

Links

Table of n, a(n) for n=1..4.

Samuel S. Wagstaff, Jr. The Cunningham Project

Prog

(PARI) is(n)=my(t=10^n\9); ispseudoprime(t) && #bnfisintnorm(bnfinit(z^2+z+1), t) \\ Charles R Greathouse IV, Jun 13 2017

Crossrefs

Cf. A004023, A003136.

Sequence in context: A172762 A203703 A068734 * A145851 A182374 A034207

Adjacent sequences: A216526 A216527 A216528 * A216530 A216531 A216532

Keyword

nonn

Author

V. Raman, Sep 08 2012

Status

approved